Packet-based data transmission is becoming increasingly popular in communication systems including land-mobile radio networks. Packet transmission opens up the possibility of improving the user's throughput by retransmitting failed data packets. Several different retransmission protocols, all based on automatic repeat request (ARQ), offer this functionality. In ARQ based protocols, when a data block fails channel decoding, it is usually stored in a local memory in the receiver. Then, upon retransmission of the data block, the retransmitted data block is combined with the failed data block previously stored in memory.
The size of the memory within a mobile terminal is preferably minimized due to the power consumption associated with large amounts of memory. Thus, a small amount of memory prolongs the operational time of the mobile terminal. Therefore, in order to provide for the advantages of packet data transmission in mobile radio networks, it is crucial to minimize the memory consumption of an ARQ protocol that includes the combination of failed and retransmitted data blocks.
One way of reducing the memory-size is to compress the symbols in the stored data blocks. Each received data block consists of a large number of symbols, and each symbol is represented in the receiver by a bit-vector of length L. Compression enables each symbol to be represented by a bit-vector of shorter length K, where K<L, which, in turn, results in a smaller memory size in the receiver.
A compression algorithm must be complemented with a decompression algorithm; however, the combination of compression/decompression algorithms may lead to increased implementation complexity. Consequently, the electrical power saved as a result of using a smaller memory may be wasted if highly complex compression/decompression algorithms are used.
Accordingly, a need exists for a method of reducing the memory consumption of stored data without adding complex compression/decompression algorithms.